時(shí)差N小時(shí):美國人的頭越來越大了

The story of human evolution goes something likethis:

人類進(jìn)化的過程大概是這樣：

Millionsof years ago, homo sapiens began to evolvefrom the prehistoric ancestor we share withourmonkey cousins.

數(shù)百萬年以前，我們和猿類共同的史前祖先開始進(jìn)化成智人。

First, we evolved the ability to walk upright.

最初，我們進(jìn)化到能夠直立行走。

Then we began fabricating moreelaborate tools.

然后，我們開始制造更為復(fù)雜的工具。

Finally, around 50,000 years ago,

最終，大約在五萬年前，

we emerged as more or less fully modernhumans with large, fully human brains.

人類以與現(xiàn)代人差不多的樣子出現(xiàn)了，擁有大而完全的人類大腦。

And since then, our craniums and the brains they harborhave stayed pretty much the same.

自那時(shí)起，我們的頭蓋骨以及它所保護(hù)的腦部幾乎保持不變。

Except that, according to one study, the skulls of some Americans have actually grown overthepast 120 or so years.

除此以外，一項(xiàng)研究稱在過去的一百二十多年的時(shí)間里一部分美國人的顱骨確實(shí)增長了。

Specifically, skulls have become larger by about eight millimeters, or a thirdof an inch.

具體說來，顱骨增大了約八毫米或三分之一英寸。

Which may not sound like much, but the growth theoretically allows for additional brainmatterroughly equivalent to the size of a tennis ball.

聽起來似乎不多，但這個(gè)增長理論上能容下差不多相當(dāng)于一個(gè)網(wǎng)球大小的額外的腦容量。

Now, before we go any further, we need to deal with a tricky detail of the study,

現(xiàn)在，在我們繼續(xù)分析之前，我們需要關(guān)注這項(xiàng)研究中的一個(gè)棘手的問題，

namely, that theresearchers looked almost exclusively at skeletons of white Americans.

也就是：研究者幾乎排除性地只觀察了美國白人的骨骼。

Why? Because, historically,mainly white Americans had donated skeletons to the collections theresearchers studied.

為什么?這是源于歷史上主要是 美國白人向研究人員捐獻(xiàn)了骨骼以供研究之用。

So whileit may be the case that the skulls of Americans of many ethnicities have grown, thestudyprovides evidence only for one group.

因此，雖然由多種族組成的美國人的顱骨可能都在增大，但這份研究僅提供了其中一個(gè)群體頭顱增大的證據(jù)。

In any case, it's not at all clear that larger skulls have translated to larger brains or togreaterintellect.

何況，更大的顱骨是否意味著更大的腦部以及更高的智慧，這仍是未知之?dāng)?shù)。

It's also not clear why the skulls the researchers looked at got bigger.

并且，研究人員所觀察的顱骨增大的原因也仍不清楚。

American life haschanged so much over the past century and a half that it will take years ofresearch to begin toidentify possible causes.

美國人的生活在過去的一個(gè)半世紀(jì)發(fā)生了如此巨大的變化以至于我們需要多年的研究方能確定可能的原因。

But, nevertheless, the observation is interesting as another detail in the complex story ofhumanevolution.

但是，盡管如此，作為人類復(fù)雜的進(jìn)化史上的一個(gè)新的發(fā)現(xiàn)，這項(xiàng)觀察結(jié)果還是很有意思的。